RTC Magazine

The increasingly complex systems in use today require increasingly sophisticated management tools. Even a desktop computer benefits from power and fan management, and the benefits increase for larger systems. The larger and more heterogeneous a system becomes, the more data must be gathered and organized to properly maintain it. Intelligent Platform Management Infrastructure (IPMI) is one standard that has been developed to address these issues.

The central player in the IPMI architecture is the management controller (MC). An MC, typically a microcontroller, monitors sensors and provides access to identifying information for one or more components. An MC runs independently of the component that it monitors. A centralized baseboard management controller (BMC) communicates directly with system management software, and allows the operator to access all of the management information in the system. The BMC also provides a system event log (SEL) that stores critical events received from other MCs.

IPMI defines a set of messages that can be sent from one MC to another. Many of the messages relay sensor or configuration information. Other messages are specific to communication between the BMC and system software. Still other messages are used to relay message data from one chassis to another. IPMI messages may be sent using a number of protocols, of which the most important is the Intelligent Platform Management Bus or IPMB. IPMB messages are sent over an I2C bus.

Using IPMI, an operator can securely establish a connection to a local or remote BMC. He can examine serial number and version information for installed components, and get a list of recent temperature or voltage spikes from the SEL. He can configure the BMC to page him if a failure condition or other event of interest occurs. The system software to accomplish this is the same, regardless of whether the system is a desktop computer or a multi-chassis data center.

ATCA Enhances IPMI

IPMI is a broad specification, but there are areas it does not address. It has only minimal support for power management, and does not support hot-swap devices at all. It is primarily a protocol and data specification, and so is not useful for hardware integration. The AdvancedTCA (ATCA) specification from the PCI Industrial Computer Manufacturers Group (PICMG) was designed to address these issues.

The ATCA specification focuses on modular computing components. It defines chassis, shelves and node boards. A chassis holds one or more shelves. Each shelf has a fan tray, a redundant pair of power supplies and slots for up to 16 node boards. Node boards may provide power and signals to rear transition modules. The ATCA specification defines connectors, voltage levels and physical dimensions for all of these components, so that components from different manufacturers will interoperate. It also extends IPMI by adding messages to support hot-swap, power control and electronic keying, or E-Keying.

ATCA defines a shelf management controller, or ShMC, which provides much the same functionality as a BMC in an IPMI system. It controls and monitors all the subsidiary MCs in a shelf, and consolidates the configuration information and sensors for all of the managed components. It communicates with the other MCs via dual-redundant IPMB, which can be either a single bus or a radial configuration (Figure 1). System software communicates primarily with ShMCs. ATCA also defines an Intelligent Platform Management Controller, or IPMC.

An IPMC typically resides on an ATCA node board, which it controls and monitors. An IPMC relays sensor events to the ShMC, and performs power and E-Keying functions in response to messages from the ShMC. A related PICMG document, the Advanced Mezzanine Card Base Specification, describes a type of node board called an AMC Carrier, which supports up to eight hot-swappable AMC modules.

The IPMI specification allows third parties to define additional types of sensors as needed. ATCA defines a hot-swap sensor type to facilitate hot swapping. Every hot-swappable entity has a hot-swap sensor associated with it. This sensor generates an event when the entity transitions from one hot-swap state to another. For example, when an ATCA node board is inserted into a running shelf, the IPMC on the node board sends a hot-swap event to the ShMC. The event message indicates that the ATCA node board has transitioned from the “not present” state to the “present” state. Although it is normally implemented in software, the hot-swap sensor can be read just like any other IPMI sensor.